The eyeball is composed of three basic layers: (1) the sclera, (2) the middle layer and (3) the retina.
The sclera is the outer layer of the eyeball. It consists of tough, white tissue that serves as the supporting framework of the eye. At the front of the eye, the sclera is continuous with the clear, transparent cornea through which light enters the eye. Behind the cornea is a small space, the anterior chamber, which contains a clear watery fluid called the aqueous humour.
The middle layer is composed of three parts: (1) the choroid, (2) the ciliary muscle, and (3) the iris. The choroid lies behind and to the sides of the eyeball making up about 80% of the middle layer. It contains most of the blood vessels that nourish the eye.
Toward the front of the eyeball, the choroid becomes the ciliary muscle. This muscle is connected by fibers to the lens, keeping the lens in place and controlling its shape.
At the very front, the middle layer becomes the iris, a thin curtain of tissue in front of the lens. A round opening in the iris, whose size is controlled by muscles in the iris, is called the pupil.
In simple terms, the cornea refracts light through the anterior chamber and then through the pupil, the entrance aperture of the eye, to the lens. The lens serves to focus the refracted light through the vitreous chamber containing the vitreous humour onto the retina, the rear surface of the eye.
Normally the fluid within the eye, the aqueous humour, is produced by the ciliary body and migrates through the pupil into the anterior chamber, the small space behind the cornea. From this chamber, the liquid migrates through the trabecular meshwork and into the aqueous veins which form fluid collection channels beneath the conjuctiva, the latter covering the front of the eyeball except for the cornea.
When the aqueous migration, described above, is insufficient to relieve the build-up of intra-ocular pressure, glaucoma results. This pressure build-up is usually due to one or more obstructions in the trabecular meshwork. Unless controlled, the high pressures associated with glaucoma ultimately leads to permanent damage of the optic nerve, the nerve formed from the sensitive fibers of the retina.
The object of the present invention is to provide a device that can be implanted permanently, simply and effectively to permit substantially normal migration of fluid out of the anterior chamber of the eye and, thus, avoid the abnormal build-up of intra-ocular pressure. Another object is to provide the implant in a manner that will also avoid excessive migration of fluid that would lead to collapse of the anterior chamber with its accompanying complications.